THAT the US Open will mark its 40th anniversary in Flushing Meadows at the tournament’s opening night Monday with Forest Whitaker emceeing performances by the cast of Tony Award-winning “Jersey Boys” and Earth, Wind & Fire . . . THAT Post reporter Max Gross celebrated the publication of his “From Schlub to Stud: How To Embrace Your Inner Mensch and Conquer the Big City” last night at the Bowery Poetry Club with a Schlub Off contest.